Quick Snapper Story

Single Species Insight

So we can run the model as a single species “snapper” complex. What we get, basically, is that no real improvement is possible for biomass without blocking also the small boats (5-15GT).

Look at the landings for each fleet (small, medium, large) when we block only large longliners from going out (darker color are simulations with more stringent effort control; darkest is 50 days out at max):

compared to when we block everybody:

Moving multispecies

Now, it may be hoped that for at least some species the result is different. From the data we have it looks like the second major product of the fishery (Pristipomoides Multidens) is mostly caught by medium and large dropliners (about 60-70%).
Is it then possible to at least protect this species by focusing on the largest boats?

The answer is, not really. What happens is that small and medium boats pick up the slack and within a few years are landing at the same level as before. Two adaptations are taking place:

• Medium boats CPUE goes up as they don’t have to compute against big boats
• Small boats drift towards more and more multidens targeting as malabaricus stock (the other main species) is consumed

Blocking medium boats too

What about blocking both medium and large boats? That actually gets us somewhere. Not really back to MSY but at least you can see a strong effect for policy. Except for malabaricus, the big 712 target which is still mostly driven by small boats.

Notice that the adaptation effects (higher CPUE for medium boats and target switching for small boats) are still there, just not enough to block some biological progress.

Cheating